The publication WO2009077537 describes a method specially adapted for the inspection of tyre treads whose tread pattern is formed by the assembly of elements having a small number of basic patterns juxtaposed circumferentially and arranged in sequence in a precise and specified manner.
The basic patterns of the tread pattern have similar shapes and have dimensions which are close to each other but not completely identical. Each type of basic pattern therefore appears several times on the circumference of the tread pattern of the tyre casing. The dimensions are chosen and the basic patterns are arranged in a carefully thought-out manner, by a procedure known to those skilled in the art, in order to reduce vibration or rolling noise.
The essence of the method described in the publication cited above is the comparison of the reference images of the basic patterns only with the image of the real basic patterns arranged on the circumference of the tyre.
Also according to this method, it is only necessary to acquire the image of the tread of a single tyre in order to obtain a sufficient collection of images of each of the basic patterns, and to calculate the average reference images of these basic patterns on the hypothesis that an anomaly is not likely to recur in all the elements having an identical basic pattern.
On the other hand, before this method is applied, the limits between the elements forming the tread pattern must be identified and located in a precise way in order to associate them with one of the basic patterns of the tread pattern.